fix: avoid double-calling a derived reference when destructuring (#18668)

Hi! This PR fixes #18666

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reason. For large changes, please create an RFC:
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- [x] Prefix your PR title with `feat:`, `fix:`, `chore:`, or `docs:`.
- [x] This message body should clearly illustrate what problems it
solves.
- [x] Ideally, include a test that fails without this PR but passes with
it.
- [x] If this PR changes code within `packages/svelte/src`, add a
changeset (`npx changeset`).

### Tests and linting

- [x] Run the tests with `pnpm test` and lint the project with `pnpm
lint`

.changeset/nervous-dolls-clean.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: avoid double-calling a derived reference when destructuring `$derived` of another `$derived` during server-side rendering

packages/svelte/src/compiler/phases/3-transform/server/visitors/VariableDeclaration.js

@@ -102,9 +102,11 @@ export function VariableDeclaration(node, context) {
 				} else {
 					const call = /** @type {CallExpression} */ (declarator.init);
 
-					let rhs = value;
+					// - cannot be a SpreadElement because refused during analysis
+					// - use args[0] rather than value to avoid visiting twice (above in const value = ... and below in for-ofs)
+					let rhs = /** @type {Expression} */ (call.arguments[0]);
 
-					if (rune !== '$derived' || call.arguments[0].type !== 'Identifier') {
+					if (rune === '$derived.by' || call.arguments[0].type !== 'Identifier') {
 						const id = b.id(context.state.scope.generate('$$d'));
 
 						rhs = b.call(id);

packages/svelte/tests/runtime-runes/samples/derived-destructured-from-derived/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	html: `<button>3</button>`
+});

packages/svelte/tests/runtime-runes/samples/derived-destructured-from-derived/main.svelte

@@ -0,0 +1,8 @@
+<script>
+	let name = $state('foo');
+	const foo = $derived(name);
+	const { length } = $derived(foo);
+</script>
+
+<!-- only needed to prevent constant folding, never run -->
+<button onclick={() => (name = 'longer')}>{length}</button>